In a contemporary vehicle driveline including a variator of the toroidal-race rolling-traction type, the key component can be expected to be a computerised control system, programmed to receive inputs of two kinds. The first such input is the drivers demand, typically for engine power and typically communicated by way of the throttle pedal. The second such input comprises a multiplicity of electronic signals, of both command and responsive type. The essential command signal will be an input representing an engine "map", that is to say a desired and programmed relationship ("control line") of engine output torque (T.sub.E) and engine output speed (N.sub.E), over the effective working range of the engine. Thus engine power (T) can be inferred from either torque (T.sub.E) or speed (N.sub.E) values for operation on the control line. The "responsive" input signals continuously supply the control system with the instantaneous values of quantities such as the actual value of N.sub.E, the actual speed N.sub.O delivered by the CVT output to the driven wheels or other point of use, and the reaction torque T.sub.R being transmitted across the variator. Appropriate processing of these inputs, by means well known in the art, enable the control system to compute other key measurements including the instantaneous ratio R being transmitted by the variator, T.sub.E and the instantaneous torque T.sub.O at the CVT output. In practice the control system will also receive further inputs relating for instance to efficiency factors and many other quantities.
The result of the many input signals, of these two kinds, that the control system receives, will in practice be only two essential output signals. One of these will be used to control the fuel supply to the engine, and the other to control the transmission.